Topic 6 and 11 – Human Health and Physiology Topic 6.6/11.4 - Reproduction
Sexual Reproduction - Overview • Basic process: make gamete (sperm) fertilizing a female gamete (egg or ovum) • Cellular union ensures that half of the genetic make-up of the resulting zygote is from each parent. • Bigger purpose: ensure genetic variation in the species. • Male and female reproductive systems adapted for sex cell production and release. • Female reproductive system ideal location for fertilization and development of embryo then fetus until birth
SPERM: acrosome, haploid nucleus, flagellum, and mitochondria EGG: cytoplasm, haploid nucleus, zonapellucida, follicle cells, and plasma membrane
Male reproductive system Vas deferens scrotum
Spermatogenesis within the testis • Occurs within small tubes called seminiferous tubules. • Near outer wall of seminiferous tubules are germinal epithelial cells called spermatogonia.
Spermatogenesis MEIOSIS MITOSIS Spermatogonia undergo mitosis to duplicate. Sperm cell production starts at puberty and continues throughout life. Millions produced each day and mitosis replaces cells that become spermatozoa. • Spermatogonia undergo meiosis to produce spermatozoa (sing. Spermatozoon). • Meiosis is reduction division. • Spermatogonia = 46 = 2n • Spermatozoa = 23 = n • 23 homologous pairs of chromosomes becomes 23 chromosomes
Three main roles of testosterone • Development of male genitalia during embryonic development. • Development of secondary sex characteristics during puberty. • Maintains sex drive. * Although males typically experience a slight lowering of sperm count as they age, fertility in males has been documented in individuals as old as 94.
Outline the role of the epididymis, seminal vesicle and prostate gland in the production of semen.
Female reproductive system Fallopian tube cervix
Outline the role of hormones in the menstrual cycle, including FSH, LH, estrogen, and progesterone OVERVIEW implantation… Endometrium must be rich with blood vessels (highly vascular) to occur. No implantation results in lose of highly vascular endometrium. Breakdown of vessels creates menstrual bleeding. Sign that pregnancy has not occurred. • Puberty in females marked by hormonal cycle known as the menstrual cycle. • On average lasts 28 days. • Times release of egg (ovum) for fertilization and implantation in inner lining of the uterus (endometrium).
Hormones from the brain Hypothalamus (regulatory center of the menstrual cycle) Gonadotrophin releasing hormone (GnRH) Triggers pituitary to release follicle stimulating hormone (FSH) and luteinizing hormone (LH) These hormones target the ovaries
Effects of FSH and LH on the ovaries One effect increases production/secretion of estrogen. Target tissue is endometrium to increase blood vessels. Another effect is the production of follicle cells and true reproductive cells within the ovary (oocytes). Chemical stimulation from FSH and LH create mature follicle cells.
FSH and LH cont… Spike in hormone levels leads to ovulation (release of oocyte from follicle). Inner ring of follicle accompanies oocyte along with glycoprotein coat (zonapellucida). Structure known as follicle and enters fallopian tube after ovulation.
Progesterone • Outer ring of follicle cells remains in ovary. • Produce/secrete hormone progesterone. • Creates glandular structure: corpus luteum. • Corpus luteum produces progesterone for 10-12 days after ovulation. • Progesterone maintains thickened, highly vascular endometrium. • Continued progesterone production keeps endometrium from breaking down and allows embryo to implant. • Negative feedback signal to hypothalamus: will not produce GnRH with high levels of estrogen and progesterone. • FSH and LH remain at levels that DO NOT produce mature follicle cells.
No pregnancy… Corpus luteum breaks down and both progesterone and estrogen levels decrease. Blood vessels of endometrium begin to rupture and menstruation begins. Drop in progesterone and estrogen signals hypothalamus to secrete GnRH Menstrual cycle begins again
11.4.8 – Compare the processes of spermatogenesis and oogenesis, including the number of gametes and the timing of the formation and release of gametes.
In-vitro fertilization • Woman injected with FSH to ensure many mature follicles are present. • Oocytes harvested surgically and sperm is donated from the male parent. • Eggs and sperm mixed and observations are made to identify fertilized eggs. • Two or three healthy embryos introduced to uterus for implantation. • Typically more than one embryo is implanted to ensure success.
Fertilization • Millions of sperm are ejaculated into a female’s vagina. • Sperm absorb fructose present in semen for added energy. • Some sperm get through cervical opening (cervix separates the vagina from the uterus). • Some of these sperm make it to the Fallopian tubes. • In the middle of the menstrual cycle a secondary oocyte may be present in the Fallopian tube. • Very small percentage of sperm ever make it to the oocyte.
Males Females Interesting facts • Average number of sperm per ejaculate (in millions) - Man: 280 - Pig: 8000 - Rabbit: 280 • Fruit flies have some of the largest gametes of any animal • Fertile life of sperm (in hours) - Man: 24-48 - Rabbit: 30-32 - Pig: 21-22 • Time to fertilization (in minutes) - Woman: 5-68 - Pig: 15 - Rabbit: few minutes • Only about 200 sperm will survive to fertilization • Ovaries can release eggs simultaneously • One ovary can release multiple eggs
How did it begin!? • Typical location for fertilization is within one of the Fallopian tubes. • Takes many sperm to get through the follicle cell layer. • Several sperm reach zonapellucida and release the hydrolytic enzymes within the acrosome. • First sperm to the plasma membrane fuses both membranes together. • Cortical reaction initiated.
Early embryo development • Fertilization triggers the zygote to begin a mitotic division (first division occurs ~24 hours after fertilization). • First 5 days mitotic divisions; moving within Fallopian tube to the uterus. • Mitotic divisions increase, embryo reaches uterine cavity and is ~100 cells in size • The embryo, at implantation, is a ball of cells known as a blastocyst.